In the related art, a robot including a robot arm has been known. As the robot arm, a plurality of arms (arm members) are connected to each other through joints, and a hand is mounted on the arm on an endmost side (lowermost stream) as an end effector, for example. The joint is driven by a motor and the arm rotates by the driving of the joint. The robot grasps a target with a hand, for example, moves the target to a predetermined place, and performs a predetermined operation such as assembly.
As such a robot, JP-A-2014-46401 discloses a vertically articulated robot. In the robot disclosed in JP-A-2014-46401, a motion for moving a hand to a position rotated by 180° around a first rotation axis which is a rotation axis (rotation axis extending in a vertical direction) disposed furthest on the proximal side (uppermost stream) with respect to a base is performed by rotating a first arm which is an arm disposed furthest on the proximal side with respect to the base around the first rotation axis.
In the robot disclosed in JP-A-2014-46401, when the hand is moved to the position rotated by 180° around the first rotation axis with respect to the base, it is necessary to provide a space having a size for avoiding interference of the robot.
Currently, a production line in which a cell for an operation by a person is replaced with a robot cell for an operation by a robot has been increased. However, a size of the robot cell for an operation by a robot is generally larger than a size of the cell for an operation by a person and the production line becomes long when the cell for an operation by a person is simply replaced with the robot cell for an operation by a robot, and accordingly, the replacement is hardly executed depending on a production site.
In addition, a height of the robot cell for an operation by a robot is great, and accordingly, when a plurality of robot cells are provided in a line, persons are hidden and accordingly, visibility is poor in the production site. When the height of the robot cell for an operation by a robot is great, the center of gravity of the robot cell becomes high and it is easily vibrated. Accordingly, the operation accuracy of the robot becomes poor and a risk of the robot cell falling down becomes high.